Perforating guns commonly used in wireline and tubing conveyed service operations for perforating subterranean oil and gas wells typically include an elongated carrier with a number of shaped charges in the carrier. Conventionally carriers are lowered in the subterranean well to a zone of interest in the formation and ignited to detonate the charges and perforate the well casing and surrounding formation. After the perforating operation is completed, a screen assembly can if needed be set in the well to control the influx of sand into the well.
In a multi-trip system, a sump packer is typically set below the zone of interest. A charge carrier is then lowered into the well to a position proximate the zone, detonated, and then removed. Thereafter, a screen assembly is installed in the well using the sump packer for proper positioning. In a single-trip system, the charge carrier is connected to the screen assembly at the screen assembly's lower end. The resulting string is lowered into the well and the charge carrier positioned adjacent the zone of interest. The charges are detonated and the carrier is then lowered through the previously installed sump packer leaving the screen supported by the sump packer in the perforated zone.
Although single-trip systems are generally less expensive to use, a problem is present regarding proper positioning of charge carriers in the casing in single-trip carrier systems. To provide maximum performance, charge carriers should be properly positioned radially in the casing at the time of detonation. Some charge are designed such that proper positioning results when the carrier is centered in the casing; in others proper positioning is present when the carrier is set off center. When charge carriers are not properly positioned radially or "centralized," the action of shape charges is diminished. In multi-trip systems positioning of the carrier is accomplished by use of mechanical centralizers. Centralizers engage the interior walls of the casing to hold the charge carrier in the proper position in the casing. However, conventional centralizers cannot be used in a single-trip system because of the restricted clearance of the sump packer. Thus, there is a need for an apparatus, which can be utilized in a single-trip system to centralize the carrier upon detonation to improve the perforation process yet allow the charge carrier to pass through a sump packer.
Another problem encountered in long carrier assemblies is detection of improper or incomplete detonation along the entire length of the carrier assembly. In single trip systems improper detonation may not be detected due to the fact that the carrier is left in the well after the attempted perforation. Thus there is a need to detect improper detonation is single trip system.